In recent years, the visible semiconductor laser has become the best light source for many signal processing systems, such as high-speed CD-ROM memory system, high-speed laser printers, bar-code scanner, and digital video-disc systems. With the range of 600 nm wavelength used in these systems, (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P four-element alloy is the most suitable material because this material has the largest energy gap among those used in the chip slot and the GaAs baseboard in the III-V group of semiconductors.
As laser output must dissolved with other optical elements, the characteristics of its output light beam appear exceptionally important. For example in an optic fiber system, smaller laser light beams' divergent angle will increase its efficiency in dissolving with fiber optics. In a digital video-disc system, it further confines far-range vertical divergent angle to be lower than 25.degree.. Unfortunately, in traditional separate-confinement-heterostructure quantum well laser, the light has to be confined as possible as in the active layer (the quantum well) to reduce threshold current. The result of closely concentrated light in the resonation cavity tends to cause very large far-range divergent angle (.theta..perp.)which reduces the dissolving efficiency with other optical elements. In addition, the dense focus of this type of light beam will also cause premature occurrence of COD, which causes reduction in the laser's life span and confines the laser's maximum output efficiency.